1. Field of the Invention
The present invention relates to a process for manufacturing a cellulose molding which is biodegradable and made from corncob meal; a plant component extracting apparatus which extracts a useful component such as cellulose from a plant, and in particularly, which can simply extract and separate a useful component without requiring a process of decomposing lignin with an agent; and a process for manufacturing cellulose acetate which is useful as a biodegradable plastic and made from bagasse, kenaf, reeds or rice straw.
2. Description of the Related Art
Biodegradable plastic is a plastic, which, like any ordinary plastic, exhibits excellent functions when in use, but which is quickly decomposed by microorganisms in a natural environment (for example, in the soil) after use and eventually becomes an organic component of earth, water and carbon dioxide, and is drawing attention in connection with the current problem of waste and the like.
Various kinds of biodegradable plastic products have been made public. Examples of such products include polylactic acids produced by dehydration and polymerization from lactic acid obtained by fermenting starch of corn, potatoes, and the like with lactobacilli. Such products are used for an agricultural multi-film, a compost bag, and the like. However, prices of raw materials and processing costs for the products are high, and these products are not necessarily rational in consideration of foodstuff situations in the future.
Although polycaprolactone, which is another example of a biodegradable plastic, may be satisfactory in physical properties as a plastic and biodegradability, polycaprolactone is also so expensive that it is difficult to use as an agricultural material and the like, and use thereof is limited to medical materials and the like.
Moreover, a plastic obtained merely by kneading corn starch with polyethylene is being sold as a biodegradable plastic. This plastic, however, is not a biodegradable plastic in the true sense of the word, since it has become clear that, although its components, which are derived from natural matter, such as starch, may be biodegradable, polyethylene does not undergo any change (decomposition). Accordingly such products are being driven out of the market despite their low price.
Thus, spreading of the biodegradable plastics, which have been heretofore known, has been slow because of their unsatisfactory performance, or because they require a complicated process for manufacture and their prices are high. The demand for biodegradable plastic products is, however, expected to increase more and more in the future for protection of the global environment, and accordingly, there is a desire for the development of products having higher performance and lower costs.
Under these circumstances, studies are being performed for a biodegradable plastic composed mainly of cellulose, which plants contain in large quantities, or a derivative thereof. However, a high cost of manufacture of this biodegradable plastic is a problem, as is the case with other biodegradable plastics.
Corncob meal, which is obtained by drying and crushing corncobs, is used as a fungal bed for growing mushrooms, an abrasive for pulse, a nest building material for animals, and the like, but is used very little as an industrial material. The greater part of the corncobs produced is thrown away as waste. Incineration is a main method for waste disposal, and thus, there are many problems with waste disposal including degradation of the environment. Study is, therefore, under way for the effective use of corncobs.
As described above, corncobs are thrown away as waste. However, the majority of a corncob is composed of cellulose (lignocellulose and hemicellulose). When corncobs are used as a raw material for manufacturing a biodegradable plastic consisting mainly of cellulose or a derivative thereof, the cost of the raw material is zero, as hardly any labor is required for gathering the raw material, and costs that have hitherto been borne by agricultural producers for waste disposal are no longer incurred. Accordingly, a biodegradable plastic made from corncobs is considered to be highly price-competitive, compared to other biodegradable plastics.
However, despite having the features mentioned, there has not been developed any bioderadable plastic consisting mainly of cellulose or a derivative thereof made from corncobs. A possible reason for this is a high cost of esterification or the like since it is difficult to separate lignin from lignocellulose, of which corncobs mainly consist.
In order to manufacture a biodegradable plastic consisting mainly of cellulose or a derivative thereof, separation of lignin from lignocellulose is required for obtaining cellulose (pulp of high quality), as described in “Overall Use and Economical Efficiency of Wood Component Obtained by Steaming Treatment and Blasting and Crushing Treatment” (online), Forestry and Forest Products Research Institute, Wood Chemical Engineering Section (retrieved on Mar. 13, 2003), the Internet <URL: http://cs.ffpri.affrc.go.jp/fbd/kenmori/mori-26.html and http://cs.ffpri.affrc.go.jp/fdb/kenmori/mori/mori-26.html>. However, the separation of lignin from lignocellulose requires many steps, i.e., grinding corncobs in a stone mill, boiling with alkali and applying a sulfurous acid treatment.
In addition to corncobs, plant seeds such as sunflower seeds, bagasse which is cane trash, kenaf, reeds, and rice straw are also promising plant raw materials for manufacturing cellulose of high quality.
Namely, agro-industrial waste, such as rice straw and bagasse which is cane trash obtained after sugar cane is squeezed to extract juice therefrom, is used very little as an industrial material, and the majority of such waste is thrown away. Incineration is a main method for waste disposal, and thus there are many problems with waste disposal including degradation of the environment. Therefore, study is under way for use of such waste.
The majority of bagasse, rice straw, and the like are composed of cellulose (lignocellulose and hemicellulose). Thus, when they are used as a raw material for manufacturing a biodegradable plastic consisting mainly of cellulose or a derivative thereof, as in the above case, the cost of the raw material is zero, as hardly any labor is required for gathering the raw material, and costs that have hitherto been borne by agricultural producers for waste disposal are no longer incurred. Accordingly, a biodegradable plastic made from bagasse, rice straw, or the like is considered to be highly price-competitive, compared to other biodegradable plastics.
Further the majority of reeds growing on the waterfront and kenaf, which is a fibrous plant, is also composed of cellulose. Therefore, when they are used as a raw material for manufacturing a biodegradable plastic consisting mainly of cellulose or a derivative thereof, it is possible to provide a biodegradable plastic which is expected to be highly price-competitive.
However, despite having the features mentioned, there has not been developed any bioderadable plastic consisting mainly of cellulose or a derivative thereof made from the aforementioned bagasse, kenaf, reeds or rice straw (which may collectively be referred to below as “bagasse or the like”). A possible reason for this is, as in the above case, a high cost of esterification or the like since it is difficult to separate lignin from lignocellulose, of which bagasse or the like mainly consists.
In order to manufacture from bagasse or the like a biodegradable plastic consisting mainly of cellulose or a derivative thereof, separation of lignin from lignocellulose is required for obtaining cellulose (pulp of high quality). However, the separation of lignin from lignocellulose requires many steps, i.e., grinding bagasse or the like in a stone mill, boiling with alkali and applying a sulfurous acid treatment.
Further, as described above, a steaming method and an extraction method with a solvent have conventionally been used as methods for extracting a useful component, such as cellulose, from a plant. However, as described above, these methods are inadequate as an extraction method used to separate and purify cellulose, in view of substantial time and labor for the separation of lignin which requires many steps and the use of an agent such as sodium sulfide, and high cost required for the separation.